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WO project with PICS sweet! (Read 2845 times)
haydenlake
Ex Member



WO project with PICS sweet!
12/26/05 at 06:20:55
 
http://www.soundsolutionsaudio.com/forum/index.php?showtopic=4982

thats where I do most of my posting so take a look and tell me what you think.

Just for ref I scaled to 1.25 that way my numbers were really easy to deal with (and for another reason you will read about below). The box is 45x45x15.5 its loud and sounds pretty nasty but if you read the post you will see why (its not a box problem).

I've read everything that's been on here about scaleing and I came to this conclusion, or thoughts anyway.

-you shouldn't use the number of inches of the driver (e.g. decware uses a 10" driver) you should use Sd as that is a better indicator of the subs size.
-I don't recall anyone talking about Vd (correct my vocab if neccessary but I recall Vd being the actual amount of volume that can be swept by the woofer) which if you think about it is just as important to modeling compression, volumes, complience, spl, and throat as anything else. (but I could be wrong)
-If i am wrong about the above can someone tell me how one speaker of Y size moving 4mm and two speakers of Y size moving 2mm will actually be any different in displacement in terms of Vd at that excursion.
-If I am right about the above we should be worrying about scaling in terms of Vd first, then second actually getting the driver to fit in the box.
-note these drivers will not fit in a 36x36box YES I TRIED! well not without moving the baffle back substantially which I wasn't wanting to do.
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60ndown
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Re: WO project with PICS sweet!
Reply #1 - 12/26/05 at 13:41:06
 
you mention distortion on the ss site? either your a super 'picky' bass head or im not? ive never  experienced distortion in a sub? ever anywhere? i cant see how your wo would distort? unless somehow a clipped signal is getting to it? solid subs with solid amplification in a solid enclosure SHOULD play solid below 100hz? maybe not as 'accurate' as some, but not distorted? Roll Eyes
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haydenlake
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Re: WO project with PICS sweet!
Reply #2 - 12/27/05 at 05:36:06
 
60 Hmm, I don't know how to explain it but the kove's (in a plain old sealed box) sound absolutlty horrible compared to my RLP or my Max. They seem to only play the higher freqs at any volume (like 50hz and above) whereas my other subs in the same box do quite well.

The part about the clipped signal could be true but I'm not sure, my receiver is about 8yrs old and it has a sub preout but I have no idea at what voltage. But I've used this receiver before in combo with the same amp and haven't noticed any problems like this. My amp should be legit since I've been using it since august with no problems and I know I have plenty of power with 2500rms at 4ohms.

I'm not writing this response to contradict you but to further understand and be able to explain what exactly it was I am hearing.

The reason I tested the Kove's in the sealed box was to make sure I had a somewhat normal listening box for them before I put them in the WO. And again, I really doubt the WO is the SQ problem.

Perhaps I am using the word "distortion" where I should just be saying "it just doesn't sound clean or good"

If you have never heard distortion in a sub what would you call it when you turn it up to the point where it doesn't sound as good as it did at normal levels but the sub isn't bottoming? this is probably what most people would refer to as distortion, (I think?)

-and yes this enclosure set up plays wayyy wayyy below 100 hrs it starts getting really loud at 35hz, but my 8's in a WO get loud at 29hz (note they have the same Fs at 34hz)

later,
b
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DirtDawg
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Re: WO project with PICS sweet!
Reply #3 - 12/27/05 at 13:12:19
 
Hey b,

I won't make an attempt to describe how distortion sounds using words, but I could write hate mail about it for days. Keep in mind that low frequencies are produced by a combination of driver and enclosure and distortions can be produced by either.

According to this old 4T (My definition)
Distortion = any tone or lack of tone that is added to, subtracted from, or in any way different from the original. I also expand that to include any deviation from the original shape of the waveform caused by numerous compromises made during manufacture of a so called low frequency transducer system.

To me, the most annoying distortion and the most audible is InterModulation (IM) distortion, which means that a tone is added to a complex signal as a result of two tones reproduced at the same time causing a third tone to be heard which is not musically related to the other two. This is usually caused after the amplifier, since most amps have decent IM specs.

The same is true with harmonic distortion (THD) except that it occurs with some harmonic consistancy and is musically related to the original tone. The second harmonic of a tone is exactly 2x the frequency of the original and follows a simple arithmetic progression (multiples: 2x,3x,4x,5x). this doesn't sound too bad as long as the 2nd is softer (less power) than the fundamental and the 3rd is softer than the 2nd and so forth, like a musical instrument. Musical instruments are usually harmonic on the even order and we are used to those. Mostly high order harmonics can become louder in a distorting driver and that increases fatigue on the listener and is unnatural sounding. Most people seem to hear odd order harmonic distortion sooner than any other type, since it so non-musical.

Nonlinearity distortion comes in many flavors. The term usually describes the inability of a driver to respond to rapidly changing voltages in the signal. A driver sometimes moves in one direction "easier" or "farther" than in the other and this causes all sorts of problems. The driver must also stop moving when there is no signal voltage, but many will continue to "ring" when they are supposed to shut up.

Power compression* is also a form of distortion, in my book, and is audible on powerful peaks as it lops off the peaks of the waveform by being too stiff to actually keep up with the changes in the signal voltage. This causes a kind of mechanical clipping and is very common. Generally power compression is heat related and increased power causes more heat and more compression. Any respectable driver should reach its Xmax without any power compression.

For that matter, any decent driver should not introduce any distortion within its rated parameters, but this is not reality. Truly excellent drivers can add as much as 5% distortion and be still be considered acceptable by current standards. Many high excursion drivers add as much as 15% or even 25% of their own anomalies to the sound. That is one of the reasons I tend to use powerful large diaphram Musical Instrument drivers with large magnets and small Xmax, in multiples, instead of one large Xmax driver to achieve the desired SPL.

Of course, it is much more complicated than this in practice, but that's a brief description of some of the basics. These types of distortion are the most noticeable to me and my ears, which have many years of use and abuse on them, but are still very sensitive for an old 4T and were well trained at one point in time. Grin

*MOD:
Just to be more clear, power compression is an inability of a driver to get louder as you turn it up. Any driver will reach a point where they can't increase acoustical ouput predictably no matter how much more amplifier power you put into them. The rules are: if you double the power input, the driver output will increase by 3dB. A driver that is in compression due to overpowering (heat increases resistance in the voice coil) or its mechanical limits (Xmax) will no longer follow the rules. Unfortunately many drivers (Power) compress long before the rated Xmax is reached.

I think I fixed all of my typos. Smiley
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« Last Edit: 12/27/05 at 15:53:24 by DirtDawg »  
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haydenlake
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Re: WO project with PICS sweet!
Reply #4 - 12/28/05 at 05:34:43
 
great response, really informative and usefull! Thanks!

So I take it you are using pro audio transducers from companies like Eminence, et al. I've noticed the inductance of these drivers seem to be far lower than your average well built high excursion driver (keep in mind I'm talking about reputable companies here). But I was talking to one guy who said that inductance isn't really all that important in a sub because of the frequencies being played. So I likened that to using a dclass (or switching amp) for a sub which should sound fine even though its really turning on and off really fast.

Any thoughts about what I posted about scaling, and if you don't want to go there I understand.

Any personal recs for pro audio drivers that are your favorite for price and performance.

The reason I've stayed away from pro audio drivers so far was because they ususally have a high Fs and I want a sub to play loud at 25hz if possible.

Why do pro audio drivers have a very small xmax yet a relatitely high xmech, I mean whats the point?

thanks,
b
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DirtDawg
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Re: WO project with PICS sweet!
Reply #5 - 12/28/05 at 10:44:38
 
b,

Do you always ask essay questions? Smiley

I can't imagine why anyone would tell you that inductance is not "all that important". As you know, all the T/S parameters that you see published are simply a starting point to try to predict what will happen in the application of that particular driver. You can never change one property without all others being affected and you can never say one property is more important than any other. Many times a lower inductance voice coil is a sign that the windings are a larger guage than an otherwise identical voice coil and that could mean higher power handling, assuming that the increased heat generated is adequately dissapated. Larger wire guage means fewer turns in the same space and that would also indicate a lower resistance. Fewer turns means decreased inductance, but that means less interaction with the magnetic field, resulting in decreased efficiency. Decreased efficiency means you have to use more power to reach the same SPL output. That's fine ..... you can handle more power, now, but have you really gained anything?  :'(

You mentioned scaling and to avoid controversy, I really "don't want to go there", but your concept of scaling for Volume Displacement of a driver may be valid in many cases. Do you scale for the maximum that a driver is capable of or the maximum that a driver is capable of without intolerable distortion? How much distortion is intolerable? How will you know until you try it?

Many here have built scaled WOs and used different methods. I used Steve's recommendation when I built a 12" WO and only scaled one dimension, using the diameter of the diaphram and it worked out fine. Some have suggested that the only way to do it correctly is to scale 2 dimensions, using the area of the diaphram as a guide. Others have scaled 3 dimensions, similar to what you suggest. Who's right? ..... I don't know ..... probably Steve when we are talking about his WO design. I do believe that scaling for a sealed or a BR cab the displacement is an important consideration, however in the WO I think the relationship between the chamber volumes is most important. I would try to keep the ratio beween the sealed and the vented chambers the same. I probably just instigated a skirmish, but additional input could be beneficial to you.

I use pro audio drivers for two reasons: I have them and I'm very sensitive to distortion. JBLs are my favorite, but I have used most top brands with good results.  There are many well made drivers available from most name brand manufacturers, but there are not really any secret bargains. You usually get what you pay for. The Goldwood comes to mind as one I have not tried. I have heard that they are a Chinese imitation of a JBL, whatever that means. Lots of people use them and are satisfied, but I often wonder if they would continue to buy a cheaper driver for half the money if they heard a real JBL in the same application and discovered, first hand, the 4 to 6 more dB of efficiency available to them. I haven't heard them at all much less side by side with what they are supposed to emulate, so my comment may be out of line. I would enjoy demonstrating my point to someone, since that's how I used to sell a few PA systems. Set up my old stuff and blow away whatever the potential buyer had and go get me new stuff. Undecided

You're wanting response down to 25Hz and that is what most would consider to be "sub" audible, so you need a subwoofer. If you're only seeing Fs in the 40s you haven't found the subwoofers, yet. Cerwin Vega, JBL, Eminence and Beyma all make subwoofers that I have used and I know sound great. There are many PA subwoofers available with a low Fs if you really want to try for a Pro Audio sound. Most people find that sound quite "dry and "flat", but I think that's the whole point. The Pro mind doesn't usually want the wetting and fluffing of a sound, making it seem more presentable and polished, coming from his speakers. (I just started another argument.)

To answer your question about the mechanical limits of many pro drivers you have to think of how they will be used ..... hours of mellow, almost restful, performance followed by moments of sheer destructive fury. They have greater mechanical limits so they won't fly apart when their powerful motors are at their peak power.

I hope some of that helps. Smiley
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« Last Edit: 12/28/05 at 10:47:13 by DirtDawg »  
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hannes
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Re: WO project with PICS sweet!
Reply #6 - 12/28/05 at 10:49:04
 
Hi,

I would say the reason for the high Xmech value is to provide a safety margin to operate in: Xmech is the mechanical limit of the mechanical system; if you reach this point, any further movement of the membrane will cause damage, for example when the voicecoil hits the cap of the magnet.

On the other hand, Xmax is the normal operation region where the driver should be able to move without too much (in theory: without any) distortion.

In a PA application, speakers will often work at or over their limits, so a good margin between Xmax and Xmech will help the speaker survive even if it is driven beyond it's capabilities.

Edit: Well, Dirtdawg was faster Smiley

Bye,
 Hannes
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« Last Edit: 12/28/05 at 10:53:27 by hannes »  
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DirtDawg
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Re: WO project with PICS sweet!
Reply #7 - 12/28/05 at 10:58:40
 
No, just started earlier. Smiley
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Hellion
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Re: WO project with PICS sweet!
Reply #8 - 12/31/05 at 13:50:54
 
It sounds as though Pro audio speakers might be just the thing for me.  I Love building expreimental boxes and using them to test whether or not my ideas work in the real world.  In fact, at this moment, I have no wokring drivers available for use in these crazy experiments.  I have no available drivers because I just blew the entire cones, voicecoils,  and dustcaps into fully separated pices by accidentally clicking on the wrong control on my computer.  (believe it or not my computer is my reciever, and I use a  Accurian HomePlug® Digital Audio Receiver/Amplifier. He he not the highest end stuff huh. I of course modded the amp and it sits in it's own cardboard box pumping out twice it's intended wattage of 50 watts.  

Anyway, I accidentally clicked on the mute button and unmuted my sound causing sudden sound to slam the woofers while the lid of the box I was tweaking was removed.  Freeair, 100watts of slightly "fuzzy" signal, and xmax of merely 75w all made a pretty ugly sound I cannot without oral sound effects explain.  It's accidents like these that make me wish that I'd never heard my friends brand new 7th order box at 13 years old.  I have done some pretty stupid stuff, but I think that tops them all. Undecided

So for my own pride's protection I may want to try getting some jbl stuff.  As long as I get full sound and what I like to call crispy response I'm there.  I guess I mean fast response.  i have build so many great sounding boxes that just couldn't do it because the bass hits in a song sounded off track and unconnected.  Is this a normal problem or some side effect of my almost home made amp?  I will be junking the amp and calling it a learning expreience when I build a box that I actually sell for more money/time than went into it. (Or when I get rich and famous, whichever comes first.) Tongue

Another thing too, I have listened to a WO in a car audio shop that sounded absolutely horrible.  Why there was one in a car audio shop I have no clue.  All I know is that they were slamming the box because it sounded like someone blew the drivers and kept playing the flapping torn remainders.  I seriously wondered who made the box and if they didn't deliberately make it sound bad.  

If you are in the South Hill Washington area check out Car Audio's sound room and ask about a dual folded horn.  They will gladly show you "The most inferior box ever made!" and tell you that you want one of thier specially designed boxes.  I have seen so many boxes that look like thier 'Specially" designed ones it makes me sick.  I personally think they didn't calculate the vas properly because I made a box once with subtracting the driver's volume from the VAS and that's close to what it sounded like.  I still thought It kinda fishy smelling.  Btw appearently they were running road master 8's in it.

I've never even heard of road master, but that's what they claim.  



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